Since SteemWorld can't know which post we will vote on, it currently shows the estimated value for a vote on a post that already got 20 STEEM.
So, if one votes a comment that doesn't have much rshares already, the green line would be somewhere on the left of the curve and the vote's amount would be much less (can be -50%). Optimal would it be to have a new setting/slider on SteemWorld, where we can choose what we want to see.
Edit
As I saw, the shown amounts in the account operations and the votes overview are really not correct currently. Will fix that today. Many things on my list...
This is an area that I really need to read up more on. Thanks for taking the time - now.... get back to your list! ;D